It is generally well known that solar energy heat collecting tubing should be dark in color or have a black or dark colored coating in order to enhance the heat absorption characteristics of the surface. A truly reflective body will reflect essentially the same spectrum which impinges upon it while a black body emits a shifted, lower energy and longer wavelength spectrum. Stated another way, the difference in energy between the incident and reemitted radiation for a black body material is the absorbed energy which goes into heat within such black body material.
In addition to the advantages of using black body absorbing materials for the collection of solar heat, it is also generally known that there is improved efficiency in having a suitable covering over the absorbing surface in order to hold the heat in the collector system by the "greenhouse effect". For example, window glass and certain plastics have selective transmitting properties where the lower wavelength spectrum of the solar energy can pass through to the heat absorbing tubing, but the higher wavelength radiation from the reradiation is not readily transmitted.
It is also generally understood that plastic materials have had various types of fillers in admixture therewith to provide improved strength, or to improve a particular characteristic. For instance, carbon particles have been used to resist ultraviolet ray deterioration. However, it is not known that conductive carbon particles have been used in tubing to provide black body heat absorption and resulting conductive or semiconductive tubing for solar heat collectors.